1. Field of the Invention
The present invention relates to a vacuum brake booster assembly for automotive vehicles, and more particularly to a vacuum brake booster assembly of the type which comprises a housing assembly including front and rear housing shells connected integrally to each other at their outer peripheral edges and mounted within the passenger compartment of the vehicle, a piston body axially movable in the housing assembly, a diaphragm member hermetically secured at its inner peripheral edge to the piston body and clamped at its outer peripheral edge by the outer peripheral edges of the housing shells to subdivide the interior of the housing assembly into a vacuum chamber and a variable pressure chamber, and a pressure control valve cooperable with the piston body for selectively communicating the variable pressure chamber with the vacuum chamber or the atmospheric air in the passenger compartment.
2. Discussion of the Background
In this type of vacuum brake booster assembly, it is advantageous that the variable pressure chamber is communicated with the clean air from the passenger compartment of the vehicle. It has, however, been experienced that there occurs unpleasant air suction noises caused by expansion and vibration of the air flowing through the control valve from the passenger compartment into the variable pressure chamber in response to actuation of the brake booster. Such unpleasant air suction noises propagate into the passenger compartment through the housing shells and are amplified by resonance of a dash panel to which the brake booster assembly is fastened. Such an undesired phenomenon is accentuated in the case that the housing shells, the dash panel and the like are structurally made as thin as possible. To solve the problems, it has been proposed to attach a dampening member to the dash panel or to increase the thickness of the dash panel. This results in difficulty in attachment of the dampening member or an increase in material cost.